Pallets, and especially wooden pallets are an essential component in the shipping and handling of commercial goods. The demand for pallets continues to increase each year, with the result that improvements in the apparatus and methods used in their construction are desirable. Pallets are constructed by assembling a number of wood, plastic or metal members to produce a frame structure with internal support members and top and bottom surfaces upon which freight is placed and the pallet rests. While pallets can be constructed by hand, the development of machine methods of pallet construction permits an individual operator to build pallets more rapidly and safely.
Machines and methods for use in building pallets are known in the art, as disclosed for example in U.S. Pat. No. 5,249,352 to Landers, Canadian Patent 1,193,424 to Viitanen & Billett and Canadian Patent 1,037,201 to Hayworth.
Typical pallet building machines, commonly called pallet jigs, such as disclosed in Landers, comprise a jig frame to position and align the members intended for assembly into the pallet, and a number of nailing guns mounted on a gantry frame. Typically pallet stringers are placed in the jig frame, then deck boards are placed in the jig frame on top of the stringers. The stringers and deck boards are maintained in position by elements of the jig frame. The nailing guns on the gantry frame are aligned with the stringers, and the gantry frame is mounted on rollers or the like so that the gantry frame can be moved along the jig frame parallel to the stringers. Thus each nailing gun is movable along one stringer, and can drive typically two nails through each deck board and into the stringer. Springs are provided to bias the weight of the gantry frame upwards so that the operator can readily move the gantry frame up and down to fire the nailing guns at the desired locations as the gantry frame moves along the jig frame.
Typically the nailing guns are fired by pressing the nose of the gun down on the board and then continuing to move the nailing gun downward to move the nose inward with respect to the nailing gun—when the nose has moved inward a sufficient distance the gun fires a nail into the board. Once the nose has moved inward sufficiently to fire the gun, it stops and then substantially no further inward movement of the nose with respect to the gun is possible.
The nailing guns are conventionally rigidly mounted to the gantry frame, as disclosed in Landers, so that the nose of each gun is at the same vertical location with respect to the jig frame. Then as the gantry frame is moved down, each nose contacts the deck board at the same time and, as the gantry frame is moved lower, each gun will fire at substantially the same time.
The conventional pallet jigs, as exemplified by Landers, operate satisfactorily when the deck boards and stringers have a consistent thickness. The surface of the deck board is then located at the same vertical location with respect to the jig frame under each nailing gun. When the gantry frame is moved down, the nose of each gun will contact the surface at the same time and will fire at the same time.
A problem is encountered however where the deck boards do not have a consistent thickness. Commonly pallets are used in applications where a rough deck surface would be satisfactory, and thus it would be more economical to use rough deck boards that were not planed to a consistent thickness. With such boards, the nose of one nailing gun will contact the highest portion of the rough board before the noses of the other guns contact the board surface. As the gantry frame is moved lower, the other noses will contact the board surface later. The first gun to contact the board will fire before the others, and prevent further downward movement of the gantry frame, since the nailing guns are rigidly fixed to the gantry frame. Where the thickness differential is large enough, one or more of the other nailing guns may not then fire and a nail is missed in the pallet.
Similarly where one stringer is slightly higher than another the same problem will occur. In order to satisfactorily use the prior art pallet jigs both stringers and floor boards must be consistently dimensioned, requiring the use of higher cost planed stringers and deck boards even where the end use could be satisfactorily satisfied by a pallet made of rough boards.